CIP Parking Garages | Corrosion Protection State of the Art

[bookowski]

I don't do a lot of parking structures so looking for some input/opinions on best practices these days. This is in the northeast. This is 1 slab on grade and then 2 elevated slabs (with multi story resi above). My early design recommendation to the client was: increased cover, low w/c ratio, corrosion inhibitor, air, sealer and traffic coating system. I had told them that epoxy bars were not required. I don't have a lot of experience with them but my impression was that the trend is away from epoxy coated bars. The client did a very similar building (same size, same block) recently where they used the above measures plus epoxy bars, so now I'm getting the 'why did our engineer on the other project use these' question. If I hadn't already said that they weren't necessary I'd probably just copy what they did but since I already told them that it wasn't necessary I'm on the fence.

For reference the summary of the concrete specs on their other project were: f'c = 6ksi, epox bars, double coat touch up on all damage, w/c = 0.35, air 6%, calcium nitrite 4 gal/yd3, moist curing only (no compounds).

Any input/opinions appreciated.

 

[Enable]

I used to live in underground parking garages all around Ontario. Here's our local account:

Epoxy was the go-to for top matt steel for a long while (bottom steel remained black though sometimes both matts were full epoxy). But a few things have happened and slowly the industry has moved away from epoxy bars.

1A) At least one early application (MTO project in Ontario) had full coating failures leading to complete debonding. The manufacturing issue was fixed and has not been a problem since but people still remember. Actually, the MTO does not use epoxy any longer and now specifies SS rebar in splash zones (see pg 15 of the bridge manual).

1B) Also, less vivid failures have been noted elsewhere (though again, from early products -1986 Florida Keys for example). This research note by the National Cooperative Highway Research Program is pretty good reading (summary below).

2) So-called "knifing shear" in galvanized rebar become a concern (also concerns with bending post-dip to some degree). Basically where a deep(ish) nick might cause greater corrosion potential at a given spot (though the entire idea is that zinc compounds migrate to the cathode, it was people's concern). People then worried about the same with epoxy coatings (damage due to handling, etc) and not being touched-up in the field (a more reasonable concern). Though in my decade or so of repairing parking garages I have never seen this happen in epoxy bars that I've dug up (with cuts and all).

3) Corrosion inhibitors in concrete mixes become more widely available and effectively replaced the need for epoxy as they provided similar levels of protection (coupled with quality concrete, C1 mixes) at less cost. This has been around for some time but only in the last 10 years have these mixes been actually workable. Used to be that we'd ask for a 150mm+/- slump with super-p but no matter what by the time it got to the other end of the line it was hard as bricks and impossible to finish. Clogged the pump like nothing else. These problems have been addressed (mostly) making it much more contractor friendly.

4) Concrete contractors or the GC control the concrete and hence enjoy a higher cost (greater markup) as compared to that cost being in the steel. So they are onboard now that the mixes are workable.

In my opinion the use of epoxy is a judgement call and can either be used or not used. There is no right or wrong though the trend is to alternatives. You just need some way of achieving a reasonable amount of durability. You may want to check out CSA S413 - Parking Structures and this white paper.

 

[bookowski]

Thanks, Enable. Exactly the kind of input I was looking for.

 

[dik]

Some issues... I've been involved in the design of many parkades. One of the first companies I worked with specialised in them. Exposure has been in the structural design of them as well as the general planning and layout of them.
[ul]
[li]high quality concrete: strength, w:c, crack control and expansion joint locations, and slump[/li]
[li]adequate concrete cover to reinforcing[/li]
[li]selection of proper structure and proper structural design[/li]
[li]good design of parkade: good slopes and drainage, proper maintenance and possible wearable membrane.[/li]
[/ul]

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[dik]

From another thread, I'm marked up the notable items.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik